1. Field of the Art
The present invention relates to an anti-squeal shim used in a disc brake for preventing a high-pitched, piercing brake noise.
2. Related Art Statement
In a common disc brake of caliper type, a piston having a circular transverse cross sectional shape is slidably received in a bore in a cylinder portion of a caliper such that the centerline of the piston is parallel to an axis of rotation of a disc rotor. Upon application of a brake fluid pressure to the cylinder portion, the piston is moved to urge a brake pad against a friction surface of the disc rotor, to thereby restrain a rotary movement of the disc rotor. In such type of disc brake, the brake pad and the disc rotor may vibrate, during application of a brake, and generate a high-pitched, piercing brake noise, so called "brake squeal". To prevent the "squeal", it has been practiced to use an anti-squeal shim having a relatively small thickness, which is interposed between the piston and a backing plate of the brake pad in order to attenuate or reduce the magnitude of vibrations of the brake pad and the disc rotor. For example, an anti-squeal shim is disclosed in Japanese Utility Model Applications which were laid open in 1980 and 1981 under Publication Nos. 55-8237 and 56-7132, respectively. The anti-squeal shim disclosed in these documents is designed to cover the entire area of the opposite abutting surfaces of the piston and the brake pad.
3. Problem Solved by the Invention
While the known anti-squeal shim disclosed in the above-identified documents is capable of preventing a squeal noise of the disc brake to some extent, its anti-squeal capability is not completely satisfactory. Other various types of anti-squeal shims have been proposed up to the present. However, none of these shims have been found satisfactory in their capability of preventing the squeal noise.